Install Visual Studio Code

Need to replicate https://github.com/betatim/vscode-binder

• Test locally
• Add the dependencies to the main environment.yml
• Install https://pypi.org/project/jupyter-vscode-proxy/
• Add the content of the postBuild script to the Dockerfile
• Deploy
• Resolve blank screen failure documented here
• Make sure code-server is launched with --disable-telemetry

See this issue for a request for a simpler setup via a conda package.